A review of available sources identified the following: a TLV-TWA and acute toxicity data (LC50, LD50, LDLo) for various routes. Data sources were selected according to the hierarchy listed in Table 3.1. Toxicity data were selected according to type of exposure, species, and route according to the hierarchies stated in Sections 3.3.1, 3.3.2, and evaluated using factors in Tables 3.2, 3.3, and 3.4. To estimate a TEEL-3 magnitude, the health hazard rating of hexachlorobenzene was also evaluated (NFPA=1), equivalent to an HHR=1 (Section 3.4.5, TEEL-3=7900 mg/m3). Although assumed durations for the LC50 were considered, the resultant TEELs were very conservative, therefore these incomplete records were not selected for TEEL development. Instead, the lowest reported rat oral LD50 was selected as the TEEL-3 basis. The TEEL-2 was derived according to Table 3.5. The TLV-TWA was selected as the TEEL-1 basis.
• TEEL-1 = TLV-TWA (0.002 mg/m³) x 3
• TEEL-2 = TEEL-3/6
• TEEL-3 = Rat oral LD50 (3500 mg/kg)
This review generated TEEL-3 and TEEL-2 values that are higher than Rev. 29A. The Rev. 29A TEEL-3 basis (rabbit LC50) and TEEL-2 basis (monkey oral TDLo) were not found during the current review. Although available LC50 data was considered, the evaluation of associated NFPA health ratings indicated these were overly conservative. Instead, the next most preferred route and species, a rat oral LD50, was selected as the TEEL-3 basis. A TEEL-2 was derived from this TEEL-3 (Table 3.5). The Rev. 29A and current TEEL-1 basis and methodology are consistent.